The invention is applicable to any oven and, in particular, to a strip floater oven which is used in conjunction with a device for applying some type of coating, e.g. paint, to a continuous element, such as a sheet of metal. An oven of this type generally comprises a number of horizontally aligned chambers which are disposed side-by-side and sealed from each other and the ambient atmosphere. A sheet of metal is guided horizontally through the coating device and then successively through the individual heat treatment chambers where it is contacted with heated gases to dry and cure the coating of paint by removal of the paint carrying solvent as a highly volatile vapor in the heated gases exhausted from the various chambers. The heated gases are impinged upon the traveling sheet of metal in each of the heat treatment chambers from a number of nozzles which are positioned vertically above and below the sheet of metal and which are normally at least coextensive with the width of the sheet of metal. At present, heated gases are brought to, and exhausted from, the individual chambers of the oven in much the manner taught, for example, by U.S. Pat. No. 3,923,449. Generally, each treatment chamber is provided with its own system for temperature and other conditioning of the heated gas circulated to that particular chamber. Spent gas including solvent vapor, is removed from the chambers in a common exhaust flue. The volume of gas exhausted from the oven is predetermined to maintain the concentration of solvent vapor at or below 25% of its lower explosive limit. Higher solvent vapor concentrations (up to 50% of the L.E.L.) may be used if the solvent vapor concentration of the exhaust gas is continuously monitored. This is done by periodically removing a portion of the exhaust gas from the common flue and measuring it for its solvent content. It can be appreciated that the solvent content of gas in the main exhaust stream is not a true reflection of the actual concentration of solvent vapor in any of the individual chambers. For example, the concentration of solvent vapor may be dangerously high in one chamber, but offset by a low concentration of solvent vapor in another chamber. The invention is directed to a simplified oven which is highly improved from existing ovens, especially as to the system for circulating heated gas to the various chambers.
Briefly stated, the invention is in an oven which essentially comprises a plurality of individual treatment chambers which are adjacently disposed in side-by-side aligned relation, and which are sealed from each other and the ambient atmosphere. Means are provided for guiding a continuous element, such as a sheet of metal, successively through the chambers for contact with heated gas being circulated therein. Means are supplied for circulating to the last treatment chamber to be encountered by the moving element, gas heated to a predetermined temperature. Other means are provided for circulating through the remaining chambers, the gas circulated to the last-to-encounter chamber and for exhausting the spent gas from the first chamber to be encountered by the moving element, so that, in effect, the same heated gas is cascaded successively through the treatment chambers from the last to the first treatment chamber to be encountered by the element as it moves through the composite oven.
Another aspect of the invention is the utilization of the spent, exhaust gas from the oven in the temperature conditioning of new gas that is suitable for circulation to the last-to-encounter chamber, such means including a fume incinerator in which the exhaust gas is heated and a heat exchanger through which the heated exhaust gas is subsequently passed for heating the new cooler gas which is then circulated to the last-to-encounter chamber.
Other aspects of the invention are the means for maintaining the proper temperature of the gas being cascaded through the oven.